Pulverizing or grinding mill



Dec. 20, 1927.

B. SCHERBAUM PULVERIZING OR GH'INDNG MILL Filed DeQ. 17, 1925 2 Sheets-Sheet 1" y @WW/Y fam/w Dec. 20, 1927. v 1,653,472 B. scHE-RBAUM PuLv'ERIzING on GRINDING um.

Filed bec. 17, 1925. 2 sheets-sheet 2 Patented Dec. 2o, 1927.1

'UNITED STATES BERNHARD sonnnnama, or wnnnr., annum.

- IV'ULVERIZING 6B GRINDING MILL/ Application led December 17, 1925, Serial No. 76,069, and in Germany December 24, 1924.

The invention relates to a pulverizer hav- The invention is, however, applicable to other forms of the grinding discs.

The invention resides in this that only the outer periphery of the grinding discs, which otherwise are exposed to the air, is sur rounded by a casing which is maintained un- 15 der a negative pressure and serves for removal. of the material treated and which passes out from the peripheral slit.

This construction is in many cases advantageous particularly because the grinding discs are continually cooled, not only on the exterior bythe atmosphere but also over their` grinding surfaces by the air drawn therethrough. lInjury to the material being treated, due to the heat generated by fric- 5 tion, isthus more or less avoided. This is a matter of importance not only in grinding meal but also in grinding other sensitive materials such as casein or the like. By the heat due to friction the metal' oi the grinding 3 discs expands so that the mill must ordinarily be more coarsely set as the temperature rises. This difficulty is dispensed with by cooling in the manner described. Moreover` the invention permits of connecting directly to the annular housing air filters for the. material ground, or of. conveying the material by means. of an air stream, which is important in pulverizing coal and in supplying powdered coal to a o pulverized fuel furnace. v

One embodiment f the invent-ion applied to pulverizing devices constructed in accordance with German Patent No. 326,110 is illustrated in the accompanying drawing, in which Fig. 1 is an end elevation of a pulverizing mill having vertical discs,

Fig. 2 is a side elevation of the arrangement shown in Fig. 1,

Fig. 3 a similar view of a pulverizer having'horizontal discs,

ig. 4 a section-through the discs shown in Figs. 1 and 2,

Fig. 5 a section through the discs shown in Fig. 3.

Fi 6 being a verticall section through the grin 'ng discs and the housin f diFig. 7 a plan view of half o the rotatable sc, 4 Fig. 8 a plan view of the associated half 60 of the fixed disc, and

Fig. 9 a diagrammatic elevation "of a.

tooth. According to Fig. 6 the material to be grounded is vfed to the mill centrally through a hopper 1 in known manner, by way of the disc 3 fixed in the housing 2. With the ,teeth of this disc engages a rotatable disc 5 mounted on the shaft 4. In the embodiment illus'- trated the discs are provided with a series of 70 preliminary breaking teeth t, which de crease in height and increase in number towards the periphery, ,and several annular rows of fine grinding teeth 8 of equal height.

s experiments have shown, such an arrangement i'sl, suited for pulverizing the most varied materials, including'both soft and also extremely hard materials, for example, corn, casein, soft Yand hard rubber, leather, coal, sandstone, glass, emery, caro borundum, cement,v clinker and so on, as also wood, straw, paper, etc.

i As will be clear from the drawing all the teeth taper towards their ends. In treating very hard materi v ls, therefore, a special ref gard must be paid to the shape-particularly of the largest breaking teeth or of the rough grinding teeth 12 located between them and the fine grinding teeth 8, if the teeth are to serve their purpose and not to 9 break 0E in a short time. Extensive investigations have shown .that the matter of most vimportance is the size of the angle formed by the tooth flanks 9, di osed radially of the centre of the discs, wit the bot- 951 tom surfaces of the teeth. i. For further explanation referenegis directed to Fig. 9 in which a breakin' tooth 7 is illustra-ted'in side elevation. e radial flanks 9 of this tooth must form such an 1 angle with the disc, and the length L of this tooth must be so'selected, that, as shown in Fig. 9 a plane E at right angle to the lane of the Hank 9 extending through the e ge a of each of these tooth anks intersects the v bottom edge b of the opposed tooth Hank,

or, as shown in dotted lines at the right hand side of the tooth represented in Fig. 9, the said plane E intersects the base of the tooth within its material portion at least within the first one-third thereof.

With tooth flanks so formed, even in grinding the hardest material theteethl do not break off. Should'they be steeper, or should the teeth be shorter, they break off immediately. If they are more inclined or if the teeth are longer, with a coarser setting of the mill the material becomes jammed between the sides of the teeth so that considerably more power is required.

The position of the tooth flanks 10 and 11 is also of importance and the angle which the tooth flank 10'makes with the surface of the rotating disc is smaller than the angle between the tooth flank 11 and the disc. The tooth flank 11 is thus steeper than the flank 10. In the fixed disc 3, Fig. 8- the relation is reversed:

It is, however, also important that the large teeth of both discs, as shown in the drawing, should be offset in relation to one another in such manner that the material to be groundin its passage from the centres of the discs to the periphery is forced to take a zig-zag path, and the large part vof the material is only gripped at a time by one tooth ring. As a result a saving in lpower and a regulated supply is obtained and stopl page prevented. The smaller material can.`

nevertheless flow olf laterally and passfrom the breaking teeth into the rough grinding teeth. Large material isl thus suitably treated by a tooth scraping on its lower face.

In the example illustrated, in addition to v three rings of breaking teeth there are provided two vrings of rough grinding teeth 12, which form a bridge between thebreaking teeth andthe fine grinding teeth 8. The ini nermost breaking tooth is mounted on thel rotating disc. p

The fine grinding teeth are also arranged in a particular manner, i. e. in esuch manner that the gaps between the fine grinding teeth Stof the one (fixed) vdisc lie on straight line radii, while the gaps betweenthe fine grinding teeth of the other (rotatable) disc 5 lie on curved lines.

This arrangement has many advantages. First, it prevents the coarse-grained material from being thrown outwards. Secondly it considerably increases the quantitative eiliciency of the device in the direction of rotation of the arcuate blank, and thirdly, on rotation in the opposite direction it facilitates particularly the fine grinding of all materials. Ifl the grinding discs are constructed in accordance with the above conditions, it is possible to make them from gray'cast iron. without adversely aifectingtheir strength in any way.

In the embodiment shown in Figs. 1 and 2 the movable grinding disc 31 is mounted on the shaft 13 which is driven by a belt pulley i32, while the stationary disc 14 is secured to an angle bracket 15 on the frame 16. The material to be ground is fed through the hopper 17. The shape of the teeth of the discs will be clear from Fig. 4, in which the bottoms of the teeth of the rotatable disc 13 lie on al hollow conical surface, and the 'points or ends of the teeth of the fixed disc '14 lie on a conical surface corresponding to vthrough the medium of an annular strip20.

To the vring housing 18 are connected at three points hose or tubular connections 21, which permit of maintaining the interior of the annular housing 18 under a negative pressure so that the material being ground can be drawn off from the peripheral gap between the two grinding discs 31 and 14. The inner. faces of the grinding -discs are thuscontinuously cooled by the suction air, whiletheir outer surfaces are also cooled sincey they are in contact with the atmosphere. If desired a fan might be fitted which would discharge a current of air againstthe outer surfaces 0`f the discs.

'The embodiment shown in Fig. 3 differs from that in Figs. 1 and 2 only essentially in this that the grinding discs are supported horizontally in the frame 16. Accordingly the shaft 13 of the rotatable disc 31 is driven preferably by a pair of bevel pinio-ns 2,2, 23, from the auxiliary shaft 24, which in turn is driven by the belt pulley 32.

The form of the teeth of the grinding discs is illustrated in Fig. 5,'from which it lwill be clear that in this construction the arrangement is the reverse of that illustrated in Fig. 4, namely the bottom portions of the teeth of the fixed disc lie on a hollow conical surface and the points or ends of the teeth of the rotating disc lie on a .conical surface similar to thehollow conical surface.. Ob-

viously the teeth in both arrangements mayripheral portions only of said discs, said housing secured to the fixed disc and pressiso I ing on the rotatable disc, substantially as and for the purpose set forth.

2. A grinding mill comprising in combination with a pair oi' grinding discs formed. with inter-engaging teeth and a centrally disposed inlet Jfor the material to be ground, a housing embracing only the peripheral portions of said discs, the teeth on said discs -tapering towards their ends in all direc-tions and increasing in number and decreasing 1n Y height towards the peripheralportions ot the discs, and the tooth flanks so shaped that a plane through the edge of one iiank and at right angles to the plane of said iank intersects at least the bottom edge of the opposite tooth Hank ^"of the same tooth and means for maintaining said housing under negative' pressure.

3. A grinding mill comprising in combination with a pair of grinding discs formed with inter-engaging teeth and a centrallyT disposed inlet fornthe material to be ground, a housing embracing only the peripheral portion of said discs, the teeth on said discs tapering towards their ends in all directions and increasing in number and :decreasing in height towards the peripheral portions, and the tooth flanks so shaped that a plane through the edge of one lank and at right angles to the plane of said Hank inter- Ynation with a pair of plane through the edge name to this speci sects at least the bottom edge of the opposite tooth, dank of the ysame tooth, and the inwardly directed flanks of the teethof the one disc making a smaller angle with the plane of the disc than the outer tooth Hanks and means for maintaining said housing under negative pressure. 4. A grinding mill comprisingin combigrinding discs formed with inter-engaging teeth and a centrall disposed inlet for the material to be ground', a housing embracing only the peripheralportions of said discs, the teeth on said discs tapering towards their ends in all directions and increasing in number and decreasing in height towards the periphery of the disc, and the tooth flanks so formed that a of one flank' and at plane of saidv flank intersects at least the bottom edge of the opposite tooth flank of the same tooth, said teeth including breaking and iine grinding teeth, said breaking teeth at least being oiset in relation to one another, substantially as and for the purpose set forth and means for maintaining said housing under negative pressure.

In testimony whereof I have fication. l BERNH. SCHERBAUM.

rig-ht angles to the signed my 

